Method of making magnetically anisotropic permanent magnets



June 21, 1966 w. MULLER 3,256,591

METHOD OF MAKING MAGNETICALLY ANISOTROPIC PERMANENT MAGNETS Filed April26, 1963 2 Sheets-Sheet l June 21, 1966 w. MULLER 9 METHOD OF MAKINGMAGNETICALLY ANISOTHOPIC PERMANENT MAGNETS MAGNETIC FIELD CROSS SECTIONOF MAGNETIC MATERIAL IN NOZZLE SECTION I FIO4 CROSS SECTION OF MAGNETICMATERIAL IN NOZZLE SECTION IT CROSS SECTION OF INVENTOR MAGNETICMATERIAL IN WERNER MULLER NOZZLE SECTION III BY 2 6. azM

United States Patent s Claims. of. 29-15% This invention relates toamethod of making magnetically anisotropic permanent magnets frompowdered materials.

It is known to prepare magnetically anisotropic permanent magnets frompowdery materials by pressing the powder in a magnetic field with abinder and then ouring the binder. Such method has been used for thepreparation of permanent magnets from Alnico powder and synthetic resinbinders. Anisotropic permanent magnets can also be formed by compressingfinely divided barium ferrite in a magnetic field without a binder andthen solidifying the shaped bodies by sintering. In this method, thepowdery particles are oriented in the magnetic field so as to produce apreferential direction in the finished magnetic body in the direction ofthe applied magnetic field. Finally, it is also known that oncompression of barium ferrite powder, without application of a magneticfield, alone by mechanic forces, wall friction, or by the platelet formof the particles, magnetic anisotropy can be produced. In this lastmethod, the direction of anisotropy is determined by the direction ofthe compression or the direction of the applied magnetic field, so thatonly simple, generally linear preferential directions can be produced.

The principal object of the present invention is to provide a simplemethod for producing non-linear, for instance arcuate preferentialdirections in permanent magnets which are prepared from finely dividedmagnetic materials.

Other objects and advantages will be apparent from a consideration ofthe specification and claims. According to the invention, an initiallyproduced preferential direction is converted into a direction of adifferent geometric shape by mechanical deformation of the form and/orsurface of the cross section of the magnet.

The invention will be better understood with reference to theaccompanying drawing wherein FIG. 1 is an elevational view of a diecompressing a magnetic powder, the mass of said powder being partlyshown in cross section;

FIGS. 2 and 3 show elevational views of subsequent steps of anotherembodiment'of the invention, and

FIG. 4 shows cross sections of the nozzle 1 in sections I, II, and IIIof FIG. 1, indicating the direction of the applied magnetic field.

Referring now first to FIG. 1 of the drawing, it represents an extrusionnozzle 1 into which a magnetic powdery material 2 is introduced indirection of the arrow. It may be mixed with a binder, preferably athermoplastic resin. In the section I, the nozzle has a Ushaped profilecross-section, as shown at 3, where said cross section is shown turnedby an angle of 90 to the plane of the longitudinal section of thenozzle. In section I, a strong magnetic field is applied transversely tothe axis of the nozzle, which produces a preferential direction asindicated in dotted lines. passes into the portion II of the nozzlewhere the U- shaped cross-section is bent to a substantially rectangularprofile 4 which receives its final form in portion III of the nozzle. Inthis way, the preferential direction of the magnetic particles is sobent as to produce approximately the form shown at 4 in broken lines.This The material then form is particularly suitable for a one-sidedarcuate magnetization as used, for instance, for portative magnets,flexible breaker strips for refrigerator doors, and the like, and hashigh values of adhesive power. Said adhesive power of magnets having aprofile 4 can be further enhanced by additional magnetization after themagnets have been extruded.

According to the invention, the powdered magnetic materials may also beemployed suspended in a suitable medium for instance water, to a paste,formed, dried, and finally sintered to a solid body.

In the embodiment of the invention illustrated in FIGS. 2 and 3, themagnetic powder 8 is formed in a molding die 5 by means of rams 6 and 7whereby. a preferential direction is impressed by means of a magneticfield 9 disposed in a direction transversely of the direction ofcompression. The thus obtained body is then transferred to a second dieIll equipped with rams 11 and 12; said rams have cooperating headsbending the magnetic body into a U-shape 13 which finished body has thena curved preferential magnetic direction 14.

In a further embodiment of the invention, the magnetic powder may hepreformed by rollers, for instance by pass rollers, and be given apreferential direction by a magnetic field or by mechanical forces, anda different geometric form of the preferential direction may be producedby additional rolling with change of the forms and/ or surface of thecross section.

As magnetic powders, preferably magnetic materials of high coercivityare used, such as ferric oxides of the type BaO-6Fe O Alnico,manganese-bismuth alloys, or manganese-aluminum alloys, if desired withconventional additions.

I claim:

I. A method for making magnetically anisotropic permanent magnets havinga desired alignment of the domains from finely divided magneticmaterials comprising shaping said powder to a magnetic body,magnetically imparting to saidbody a preferential direction ofmagnetization, and subsequently mechanically deforming said magneticbody to change it to a different geometric shape and transform saidpreferential direction to a different direction.

2. The method as claimed in claim 1 wherein said magnetic material isused together with a thermoplastic resin binder.

3. The method as claimed in claim 1 wherein said magnetic material isused as an aqueous paste.

4. The method as claimed in claim I wherein a magnetic material of highcoercive force is used.

5. A method for making magnetically anisotropic permanent magnets frompowdered magnetic materials comprising passing said material through anextrusion nozzle, providing in said nozzle a first and a secondcompression zone, said zones having dissimilar cross sections, andimparting a preferential magnetic direction to the material passingthrough said first zone, said preferential direction being changed to adifferent direction on passage of the material through said second zoneof dissimilar cross section.

6. A method for making magnetically anisotropic permanent magnets frompowdered magnetic materials comprising preforming said magnetic powderin a die to a shaped body, imparting to said powder while it ispreformed a preferential magnetic direction, and compressing said shapedbody in a second die to a final magnetic body having a cross sectiondissimilar to that of the shaped body, thereby changing saidpreferential magnetic direction to a different direction.

7. A method for making magnetically anisotropic permanent magnets frompowdered magnetic materials comprising rolling a powdery magneticmaterial to a first shape, imparting to said powder While it is rolled apreferential magnetic direction, and subsequently rolling said firstshape to a final second shape having a cross section dissimilar to thatof the first shape, thereby changing said preferential magneticdirection to a different direction.

8. A method for making a flat substantially rectangular magneticallyanisotropic elongated permanent magnet having its N and S poles at thesame side of one of its flat surfaces comprising extruding a magneticpowder 10 References Cited by the Examiner UNITED STATES PATENTS OTHERREFERENCES wt hat you can do with flexible magnets Product EngineeringJanuary 9, 1961, pp. 65-68.

JOHN F. CAMPBELL, Primary Examiner.

1. A METHOD FOR MAKING MAGNETICALLY ANISOTROPIC PERMANENT MAGNETS HAVINGA DESIRED ALIGNMENT OF THE DOMAINS FROM FINELY DIVIDED MAGNETIC MATERIALCOMPRISING SHAPING SAID POWDER TO A MAGNETIC BODY, MAGNETICALLYIMPARTING TO SAID BODY A PREFERENTIAL DIRECTION OF MAGNETIZATION, ANDSUBSEQUENTLY MECHANICALLY DEFORM-